We are attempting to understand the chromosome organization in Drosophila. In view of the widespread occurrence of middle repetitive sequences which appear to be identical or nearly identical, we plan to identify restriction segments corresponding to a small defined region of the chromosome by the following procedure. By genetic techniques, flies are constructed having multiple duplications for a short region of the genome, corresponding to only 4-10 bands. DNA is isolated, and subjected to two-dimensional restriction analysis (Potter, Thomas, Cold Spring Harbor Symposium, 1977, in press). These restriction segments derived from the duplicated region will appear with 4-8 fold intensity (depending on the number of duplications achieved). These are then isolated from the gel, amplified and nick-translated and used as probes into further isolate the adjacent sequences, and to verify their location by in situ hybridization to the polytene chromosomes. Our objective is to make a complete restriction map of a number of adjacent chromomeres containing genes of developmental significance. To summarize, our objectives remain the same as described for GM-21740, but the approach will be relying on 2 dimensional restriction analysis. The last two years of this grant will be pursued in a new location at the Scripps Clinic & Research Foundation in La Jolla, California.